The goals of our Center, Modifiers of FMR1-associated disorders: application of high throughput technologies, are targeted to the RFA research area to Advance the understanding ofthe pathophysiology of FMR1 Related Conditions. The completion of the proposed aims from the three research projects will lead to the identification of the genetic basis of variable expressivity or incomplete penetrance of FMRI - associated conditions by searching for modifying loci by whole genome sequencing (WGS) of 200 subjects in each of the three projects. Project A will focus on the variable expression of epilepsy among boys with fragile X syndrome (FXS), a co-morbid condition that occurs among 15% of affected boys and we speculate that variation elsewhere in the genome is responsible. Likewise, Project B will focus on the incomplete penetrance of fragile X tremor/ataxia syndrome (FXTAS) in men, a neurodegenerative disorder among those with the premutation (PM). Project C, the topic of this project proposal, focuses fragile X association primary ovarian insufficiency (FXPOl), which manifests in 20% of PM carriers as premature ovarian failure (POF), or cessation of menses prior to age 40. POF leads to infertility and estrogen-deficiency related disorders usually reserved for the aged. Other PM carriers have a normal reproductive life span. Our goal is to identify and understand the extent of the epistatic effects of modifying genes on these three Mendelian disorders. We will recruit FMRI repeat mutation carriers from the tails of the phenotype distribution and compare their genetic variant profiles obtained from WGS. Specifically for this proposed project, we will obtain WGS on the cohort of 200 fragile X premutation carriers (100 male premutation cases with onset of FXTAS symptoms before age 65 and 100 male premutation controls with minimal symptoms of FXTAS after age 70, matched by repeat length to cases). Prioritized candidate genes from WGS will be validated and then functionally assessed using high throughput phenotype assays in Drosophila. This project will equally use shared Center cores: Recruitment Core B and the Genomics and Analytical Core C. We anticipate that identified modifying genes of FXPOl will provide insight into interventions for women ovarian insufficiency.